The present invention relates to a composition comprising a vinylidene fluoride polymer, such as polyvinylidene fluoride, and a blowing agent, and also to a process for the manufacture of cellular or dense articles from this composition.
It has already been proposed to produce compositions comprising a polymer derived from vinylidene fluoride, and a blowing agent, which can be used for moulding finished or semi-finished articles of cellular structure.
Thus, German Patent Application No. 2,827,396, filed on June 22nd, 1978 in the name of PCUK-PRODUITS CHIMIQUES UGINE KUHLMANN, divulges, in Example 17, a composition consisting of polyvinylidene fluoride containing 1% by weight of a blowing agent, in this case azodicarbonamide.
According to this example, this composition does not permit the injection moulding of cellular articles of acceptable quality, because they have blackish streaks which are evidence of thermal degradation of the polymer. To avoid this unacceptable disadvantage, according to this same example, it is appropriate to incorporate 1% by weight of low-density polyethylene and 1% by weight of polytetrafluoroethylene into the moulding composition. However, these ingredients are capable of modifying certain properties of the finished articles, and it is not therefore possible for the compositions in which they are present to be used for every application.
It is therefore apparent that it is not sufficient to incorporate a conventional blowing agent into a vinylidene fluoride polymer for manufacturing cellular articles.